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Multicarrier direct-sequence code-division multiple-access (MC-CDMA) overlay has been proposed to be used for ultra-wide-band (UWB) communications. Interference reduction and interference suppression are the key issues for sharing the spectrum in harmony between the established narrow-band systems and e overlaid UWB system. In this paper, investigation is carried out on the use of compromising measures incorporated to the MC-CDMA overlay to meet these goals, as well as on their impacts to e involving parties. At the transmitter, interference reduction to e established narrow-band systems is done by using notch filters. multipath Nakagami fading channel is assumed. At the receiver, e interference suppression from those narrow-band systems is filled by minimum mean square error (MMSE) detection technique. Numerical results show that precombining MMSE with selective-maximal combining provides the UWB system with much better performance than the receiver made up of notch filter in cascade with code correlator. [ABSTRACT FROM AUTHOR]

In this letter, the performance of multicarrier code-division multiple-access (CDMA) systems is studied in the presence of narrowband interference for future ultra-wideband (UWB) communications. A Nakagami fading channel is assumed, and notch filters along with diversity techniques are used in the multicarrier CDMA receiver. A complete performance analysis of error probability is given. It is shown that when the number of subcarriers jammed by narrowband interference is small, the multicarrier receiver without notch filters can work well, due to the gain of frequency diversity from nonjammed subcarriers. On the other hand, when the number of subcarriers jammed by the narrowband interference is large, using notch filters can improve the multicarrier system performance significantly. [ABSTRACT FROM AUTHOR]

In this paper, the effect of imperfect channel estimation on the transmit diversity based on space-time block coding for the downlink of a direct-sequence code-division multiple-access system is studied. Two transmit antenna and one receiving antennas are employed. However, the results of this paper can be extended to the system with more receiving antennas. Each channel is modeled as frequency-selective Rayleigh fading and the pair of channels corresponding to two transmit antennas are mutually independent. Both spatial diversity gain and multipath diversity gain are obtained in the system. The system performance is evaluated in terms of bit-error rate under the perfect and imperfect channel estimation. A pilot-assisted channel-estimation scheme with one common spreading code sequence is exploited. It is shown that the inaccurate channel estimates suffering from multiple access and multipath interference significantly degrade the system performance and can be effectively improved by use of a simple low-pass filter. The investigation of the power ratio of pilot to data channels illustrates that the base station should dynamically adjust the transmit power of the pilot channel according to the varying system configurations in order to achieve the best performance. [ABSTRACT FROM AUTHOR]

Proposes a multicarrier direct-sequence/slow-frequency-hopping code-division multiple access systems. Description on the system models; Performance analysis; Discussion on the numerical results.

Examines the effects of power control error on the performance of the code division multiple access overlay system which is overlaid on downlink by a narrow band signal. Description of the downlink system model; Analysis of the open-loop power control in the presence of narrowband interference; Overview of numerical results.

Focuses on the use of a suppression filter for a direct-sequence code-division multiple-access (DS-CDMA) system operating over a Rayleigh fading and sharing common spectrum with a narrow-band waveform. DS-CDMA system and channel models given; Up-link bit error rate (BER) performance of CDMA system; Parameters that influence CDMA system BER performance.

This paper investigates the average bit error rate performance of a direct sequence code division multiple access system operating over a multipath Rician fading channel (which models indoor radio propagation in factories). We consider both phase shift-keying modulation with coherent demodulation and differential phaseshift-keying modulation with non-coherent demodulation. Predetection multipath diversity (maximal-ratio-combining for coherent reception and equal gain combining for non-coherent reception) is considered for improving the BER performance. [ABSTRACT FROM AUTHOR]

Abstract: The Multi-Carrier Code Division Multiple Access (MC-CDMA) is becoming a very attractive multiple access technique for high-rate data transmission in the future wireless communication systems. This paper is focused on the joint channel and power allocation in the downlink transmission of multi-user MC-CDMA systems and considers the throughput maximization problem as a mixed integer optimization problem. For simple analysis, the problem is divided into two less complex sub-problems: power allocation and channel allocation, which can be solved by a suboptimal Adaptive Power Allocation (APA) algorithm and an optimal Adaptive Channel Allocation (ACA) algorithm, respectively. By combining APA and ACA algorithms, an adaptive channel and power allocation scheme is proposed. The numerical results show that the proposed APA algorithm is more suitable for MC-CDMA systems than the conventional equal power allocation algorithm, and the proposed channel and power allocation scheme can significantly improve the system throughput performance. [Copyright &y& Elsevier]